The invention concerns delayed gelation systems which can be used in particular for water control processes in the oil industry and, more generally, the selective treatment of formations.
This type of process for some underground formations crossed by injection or production bore holes, is well known in its principle by those skilled in the art, as well as the very difficult problems which it raises. It will be useless to describe those operations here. This invention is concerned with selectively plugging the pores of an underground zone without plugging the oil producing layer.
It was first proposed, in the U.S. Pat. No. 3 614 985, using urea and aluminum chloride to cause a delayed aluminum hydroxide precipitation.
The French patent application no. 85-10272 applied July 2, 1985 proposes using aluminum hydroxychloride which allows accurately controlling the precipitation time, the structure and the morphology of the precipitate.
The French patent application no. 86 06434 applied Apr. 30, 1986 proposes using hexamethylenetetramine and the French patent application no. 86 14089 applied Oct. 8, 1986 recommends the adjunction of an adjuvant for the activator (sodium cyanate).
The teaching of all the above mentioned documents is incorporated here as a reference and those skilled in the art can refer to those.
The above discussed techniques have reached an efficiency and an accuracy which are satisfactory taking into account the extreme difficulty of the technical problem raised.
An object of the invention is to further improve some aspects of these techniques and to substantially reduce their cost which has become an absolutely determining parameter in the oil industry.
One of the major inconveniencies of the water control techniques generally is their very high cost. This is caused by the necessity of using large volumes of fluid to obtain the desired effect. Namely, it is very often necessary to treat the permeable basin over a several meters, possibly several tens of meters, depth and not limit a plugging process to the immediate surroundings of the bore hole.